Laurent Fabius, who announced Wednesday that he was stepping down as French foreign minister, achieved soaring international stature for his role in negotiating the Iran nuclear deal and for finding rare international consensus on the environment.

A wealthy man who hails from a long line of art dealers, Fabius holds the distinction of having been France's youngest-ever prime minister, a post he took up in 1984 at the age of 37.

He remained a Socialist Party heavyweight, ending his political career in the ornate hallways of Paris’s Quai d'Orsay foreign ministry as his country's top diplomat, a post he held from 2012 despite a relationship with President François Hollande that was said to be professional but not friendly.

According to one member of his entourage quoted by French daily Le Monde, “Hollande fears and respects Fabius, and Fabius despises Hollande but holds his function as president in high esteem.”

His time as foreign minister was marked by some notable successes, including brokerage of the Iran nuclear deal in 2015 and presiding over the COP21 environment summit in Paris later that year.

Fabius stands down frustrated by his inability to resolve an enduring crisis: the Syrian civil war.

His tough line on Syrian President Bashar al-Assad and calls to arm the country’s moderate opposition were not supported by other Western countries, notably the USA, leaving him frustrated with American leader Barack Obama, who he said was “good at talking, but not so good at acting”.

Getting there meant overruling an earlier US-backed draft deal, tabled in Geneva in November 2013, which he described at the time as “cheap”.

His intransigence was hailed by hardliners in Washington, including US senator and former presidential candidate John McCain, who tweeted “Vive la France!” in gratitude for Fabius’s stubborn refusal to accept any half measures.

Fabius was blasted, however, by those who argued that failure to conclude a deal quickly would harm French interests.

“How much criticism France endured at the time, such as accusations that France would pay for its intransigence,” Fabius told Le Monde. “The proof that France got it right is that we were one of the first countries visited by Iranian President Hassan Rohani [after the deal was signed].”

Saving the planet

Fabius’s final big project, one which is likely to seal his legacy, was a truly international deal to save mankind from global warming.

Initially lukewarm in his approach to environmental issues, Fabius gradually embraced the cause and studied climate science intensely for two years before the 2015 talks.

As host of the global climate talks in November and December 2015, just after the November Paris attacks that threatened to overshadow the event, he presided over 13 days of gruelling talks, amidst persistent rumours that he was suffering from Parkinson’s disease.

But in the end he secured the agreement of 195 nations to transform the energy system underlying the world economy.

"It's rare in life to be able to move things forward on a planetary level," a visibly moved Fabius said as world leaders gave him a standing ovation at the culmination of the summit.

Fabius will stay on as COP president for the next few months, as the UN body moves towards implementing the Paris deal signed in December 2015.

Syrian regrets

If there is one area where Fabius has struggled, it is the Syrian conflict. From 2013, Fabius insisted that the removal of Assad, who enjoys Russian and Iranian support, was necessary to end the civil war.

France also called on the world to arm and support moderate rebel movements to fight both the Damascus regime and the Islamic State group, but France was left diplomatically isolated when the US backed down from its threat to bomb regime targets in 2013.

Announcing his resignation from government on Wednesday, a frustrated Fabius told parliament that “you don't get the feeling that there is a very strong commitment" from the US in Syria.

"There are words, but actions are different and obviously the Iranians and Russians feel that," he said as foreign ministers prepared to meet in Munich, Germany, for another round of peace talks.

The talks come as forces loyal to Assad, supported by Russian air strikes, continue their offensive against Western-backed rebels, an assault that has pushed hundreds of thousands of civilians to flee rebel-held parts of Syria's largest city, Aleppo.

"When you add [Assad's] brutality, Russia and Iran's complicity and American ambiguity, you get the drama taking place in Aleppo," Fabius said.